This invention relates to pipe tools and more particularly to a pipe beveling machine with improved operation and structure.
In pipe beveling, a beveling machine is typically mounted within the pipe to be beveled, by means of a mandrel device that secures the machine in relation to the pipe by engaging the inner walls of the pipe. A draw bolt is provided and tightening of a draw nut causes portions of the mandrel to expand and engage the pipe. Heretofore, if the draw bolt was to break, components of the mandrel would fall off, into the pipe. Such an accident can be annoying and difficult to remedy, as the component might end up at rest in a bend in the pipe a great distance from the beveling site. The particular resting site would have to be located, and the pipe cut open to retrieve the components. To address this issue, some mandrels employ a spring that allows expansion of components for engaging the pipe walls, but still holds the components to the mandrel. However, this is not always satisfactory, as the spring can break (and fall off), and if the draw bolt does break, often the surrounding mechanisms that hold the spring also fall off, into the pipe.
In beveling and facing devices, it is desirable to have a backlash free engagement between the driving and driven portions of the devices. There are numerous designs of mechanical keys that fit into correspondingly shaped grooves or "keyways" of mechanical members to lock the mechanical members from moving relative to each other in one or more axes. The Woodruff, Saddle, and Gib-head keys are some of the more common designs. Most of the mechanical industry's keys are of a single piece design and are not adjustable. This means that they must be designed with somewhat relaxed tolerances that allow for friction fit and installation. In high torque situations this "loose" fit is undesirable as it leads to accelerated wear resulting in "backlash" (movement of one element relative to the other) and a greater potential for key failure due to the higher shear forces encountered with "backlash". Conventional mechanical keys do not address this problem. If backlash is present, given the high torque situations, "chatter" can result, giving a rough or poor cut or faced portion.
A particular application for these keys is seen in such high torque applications as beveling tools for pipes or facing tools. A mandrel clamps to a pipe and a non-rotatable power unit is slideably mounted on the mandrel. The power unit has a rotatable portion that holds and rotates a cutting tool to "face" the pipe. The power unit itself does not rotate and is held from doing so by locking keys that are interposed between the axial mandrel grooves, and keyways cut into the non-rotatable power unit. These locking keys also mount the power unit onto the mandrel. The power unit slides axially along the mandrel to feed the cutting tool into the pipe. When in operation, these locking keys experience high torque loads in maintaining the stationary position of the non-rotatable power unit in response to the reactionary force experienced as its rotatable portion faces the pipe. These keys are subject to extreme shear forces and wear quickly. As they wear there is more "backlash" movement developed between the non-rotatable power unit and the mandrel, thereby increasing the shear forces and accelerating wear. Most of the locking keys in the industry do not accommodate for wear and are not adjustable, requiring frequent replacement.